In The Mystery of the Torn Parachute, Captain Mackenzie was a Spey fishery board official who lived in the Grey House on the Grantown Road near Knockando in Morayshire. He managed motor cycle baillies who patrolled the roads at night on the look out for Salmon poachers. When Biggles was investigating the mysterious appearance of a piece of French parachute silk up a tree in Morayshire, Mackenzie was able to provide Biggles with details of vehicular movements in the area during the time period he was concerned with. From Mackenzie's records, Biggles' suspicions were drawn to one Mrs Williams. Mackenzie told Biggles that Mrs Williams was an Englishwoman, a widow who had come up from London and lived alone. She was, he said, a nice lady, and not much of a worry for him. However Biggles remained suspicious as, in his opinion, two o'clock in the morning, seemed an unusual time for a young woman living alone to be driving about.